This section examines objectives of numbering, the regulatory framework for allocation of numbers, implications of technology trends as well as the respective key points and recommendations.

Practice Notes

Reference Documents Objectives of numbering

The objective of a numbering plan is to establish a unique identification of subscribers and providers of services. The numbering plan for the telephone network is only one out of several numbering plans each facilitating communication between different users connected through a common infrastructure. Other numbering plans include numbering plans for data networks, such as the IP-numbers used for identification of users of the Internet. E-mail addresses and domain names may also be seen, as a sort of numbering systems as they also are used to provide users with a unique identification code. Regulatory framework for allocation of numbers

Telephone numbers are designed by the national telecom regulators according to the E.164 numbering plan (see the practice note on the E.164 numbering plan). For technical reasons numbers have been designed according to their geographical location in such a way that subscribers connected to the same local exchange share the same area code.

A numbering plan can be either open or closed. In an open numbering plan special arrangements are made for local calls, so the dialer only needs to include the area code in long distance or international calls. In a closed numbering plan the same number of digits must be dialed in all national calls.

Most numbering plans reserve special series for different kinds of calls or services. For instance special prefixes are used for mobile numbers in India and in Brazil. Each operator may also have its own prefixes, as in Colombia. Many countries have reserved 800 and 900 numbers for freephone and value added services.

Thus numbers do not only serve as a tool for unique identification, they also provide information on location, type of service etc. This information is often necessary in order to know the tariff for the call.

The international regulatory framework for administration of IP-addresses is headed by ICANN and completely different from those in the E.164 numbering plan. For more information about the international regulatory framework for the administration of IP-addresses, please see the Practice Note on ICANN. At the national level similar models of self regulation have often been established in order administrate the national allocation of IP-addresses and domain names.

Practice Notes

Reference Documents Implications of technology trends

The major implications on numbering of the four technology trends and implications mediated via changes in the market structure are depicted below:

Technology implications on numbering

Mobile communication

Development of next generation network infrastructures

Increasing use of IP and other packet switching infrastructures


Implications caused by via changes in market structure

Geographical numbering plans were once a necessity, but today a growing number of countries have stopped demanding a relation between numbers and geographical location. This enables a more efficient use of an increasingly scarce resource, and facilitates number portability for subscribers moving to a new location. Moreover, convergence between local and long distance calls makes it less necessary to inform about geographical location of subscribers.

The growing penetration of mobile subscribers has encouraged this development. First, growth in the number of mobile phone has increased the total demand for numbers, which potentially can lead to number scarcity in some regions. Second mobile phones are used from many different locations and numbering and tariff schemes for mobile phones are most often national and not regional.

Geographic numbering plans and even national numbering plans are also challenged by VoIP. VoIP services can be provided at any location where the Internet can be accessed. The VoIP operator does not need to be present in a particular country. The operator can acquire numbers from the UK numbering plan, for example, and offer them to subscribers in any other country.

A particular problem related to VoIP is tracing of emergency calls. At present, it is not possible to trace an emergency call from a VoIP phone. The call may therefore be routed to a wrong location (even in a wrong country). It is possible to assign a physical address to a VoIP number, but the same VoIP number may be used from many different locations just as mobile phones are (nomadic use).

Another issue related to mobile communication is cross portability of numbers. Number portability is essential for new market entrants, as subscribers are much more reluctant to change operator if they are unable to keep their number. Number portability is important for both new market entrants offering their services by use of existing technologies, and for operators building their service provision on new alternative infrastructures.

Number portability between fixed and mobile services could potentially lead to increased competition between fixed and mobile services, as it then becomes more attractive to give up the fixed-line subscription and substitute with a mobile. Cross portability will lead to less transparency in tariffs, as it will become impossible for a consumer to distinguish between calls to fixed and mobile phones. A similar problem arises with respect to national and in particular international settlements between operators. As long as termination charges in fixed and mobile networks differ, it is necessary for operators to distinguish between calls to fixed and mobile subscribers.

Furthermore it is doubtful if cross portability is necessary to facilitate competition between fixed and mobile services. There are now more mobile than fixed subscribers in many countries. This indicates that mobile phone services have been able to compete without offering number portability.

The situation may be different with regard to VoIP. The penetration of VoIP subscribers is still much lower than that of mobile subscribers, and the service offered by VoIP is more similar to fixed telephony. In this case lower prices are the main advantage. Therefore cross portability between POTS and VoIP will be an important measure in order to facilitate development of VoIP.

Convergence between Internet and telephony implies a need for a coordination of numbering plans. VoIP can be offered without allocation of numbers from the E.164 numbering plan. Domain names, IP addresses or service specific identification addresses may be used instead. However, it is not possible to call a VoIP subscriber from an ordinary phone without allocation of a number which can be recognized by the traditional fixed telecom network.

ENUM – tElephone Number Mapping addresses this problem by offering a method for conversion of telephone numbers to IP-addresses and visa versa. ENUM is supported by a number of VoIP operators and is being implemented in a number of countries. So far three countries (Austria, Poland and Romania) have reached the stage of production, while trials are implemented in Finland, France, Germany and Japan (Ripe ENUM working group ENUM is supported by international organizations such as ITU and the EU and is expected to be the future standard for connection between IP networks and PSTN networks.

However, current experiences have revealed a number of critical issues related to use of ENUM. All of these are related to the fact that ENUM is developed outside the formal regulatory framework. ENUM may be adopted through agreement among major Internet service providers without any Governmental involvement. On the other hand the E.164 numbering plan is administered by the national regulatory agencies. Therefore the allocation of responsibilities regarding the administration of E.164 numbers and the administration of the E.164-subdomain within .arpa must be clearly defined* Annette Hillebrand a.o.: Business Models and ENUM – Opportunities and Challenges EuroCPR 2005..

Practice Notes

Reference Documents Key points and recommendations

    • It is no longer a technical necessity to use location dependent numbering schemes. Moreover use of mobile phone services and VoIP implies that the same number can be used from different geographical locations. Some countries have therefore introduced national numbering plans allowing subscribers to maintain their number if moving to another region (geographical number portability)
    • Numbers are used as a unique identification of PSTN subscribers as well as subscribers of mobile services or VoIP. If different charges are applied for calling different types of subscribers, consumers may demand clearly distinguishable numbers for PSTN, mobile and VoIP subscribers, but such a numbering plan will prevent cross portability and may hamper competition between services.
    • Translation between IP numbers and the E.164 numbering plan used for telephone services is provided by ENUM. ENUM enables Internet based users to communicate with telephone subscribers and vice versa. ENUM is being implemented in a number of countries, but it also is subject to being replaced in the future as a result of technological improvements.

Practice Notes

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